The proliferation of smartphones and other wireless devices has led to ever-increasing demand for wireless spectrum. In an effort to ameliorate this problem, the U.S. Federal Communications Commission (FCC) has established a shared-spectrum service in the 3550 to 3700 MHz band (i.e., 3.5 GHz band). This band has been traditionally reserved by the U.S. Department of Defense for military use, for example, by military radars on navy ships. The FCC has recently made the 3.5 GHz band available for a commercial radio service called Citizens Broadband Radio Service (CBRS). Because the spectrum is shared, some mechanism must be adopted to ensure users within the same spectrum do not interfere with each other, and that users with higher priorities have guaranteed access to the spectrum in a situation of a conflict.
Using the 3.5 GHz band as an example, a three-tiered model has been proposed and adopted by the FCC in an effort to protect existing users of the band, as illustrated in FIG. 1. As shown in the figure, the top tier belongs to incumbent access (IA) users, such as federal and non-federal incumbent systems, who have the highest priority to use the 3.5 GHz band. Between the incumbent users and non-incumbent users (typically public users) are one or more Spectrum Access Systems (SAS), which coordinate and facilitate spectrum sharing among all of the users in the band. Then among the public users, some may obtain higher Priority Access (PA) under a Priority Access License (PAL), while others may operate without a license under General Authorized Access (GAA), GAA users have the lowest priority within the allocation.
The SAS may facilitate efficient spectrum allocation among the three tiers shown in FIG. 1 by ensuring that communications from wireless devices (“user equipment” or “UE”) in a lower-priority access tier do not interfere with communications of those in a higher-priority tier. The SAS may accomplish this by monitoring interference and frequency usage in the shared spectrum, and dynamically allocate frequencies for devices to use within the spectrum.
In this context, a “frequency” broadly refers to a frequency band, a frequency channel, a frequency within a band or channel, or a signal at a particular frequency (such as a carrier signal), and unless otherwise noted these terms may be used interchangeably. A “connection” broadly refers to any communication of information, such as voice and/or data, between devices using one or more frequencies. “Spectrum” broadly refers to frequencies that may be used to establish connections.
The SAS coordinates and manages spectrum sharing among the incumbents, PAL systems, and GAA systems, by dynamically allocating spectrum to the PAL and GAA user-equipment devices. However, current PAL and GAA devices are not designed to dynamically switch frequency channels during an ongoing connection in the wireless access system. Thus, anytime the SAS allocates new frequency channels for the PAL or GAA devices to use in the shared spectrum, these devices may not be able to switch frequency channels efficiently, quickly, or smoothly with minimal disruption to the end user's experience. Moreover, the three-tiered model may pose significant challenges to lower-priority users when they must discontinue using a frequency so it may be used by higher-priority users, for example during emergencies, or in other situations of conflict with higher-priority users, with little to no warnings.